1. Field of the Invention
The present invention relates to automatic control systems with feedback, and, more particularly, to proportional/integral/derivative automatic control systems using a feedback pulse train from a target system to be regulated.
2. Description of the Related Art
Automatic control systems with feedback are used to regulate the operation of a target system, such as a paper transport assembly in a printer with a regulated rotational speed of a roll. One such control system is known as a proportional/integral/derivative (PID) control system which provides a control signal to the target system which depends upon an error signal (proportional, KP) the integral of the error signal over time (integral, KI), and the change in the error signal over time (derivative, KD). A weighting or gain constant is associated with each of three error terms KP, KI and KD. A transfer function utilizes these three error terms to generate a control signal used to control the target system. Examples of such transfer functions include:
Continuous Transfer Function:GPID(S)=KP+KI/S+KdS 
Discrete Transfer Function:GPID(Z)=KP+KI[Tz/(z−1)]+KD[(z−1)/Tz]where:
T—sampling period
KP—proportional gain
KI—integral gain
A conventional PID control system as described above may be carried out using a computer, such as a personal computer (PC). A problem with such a conventional PID control system is that the target system typically provides digital feedback output signals in a form which cannot be directly utilized by the PC. For example, if the target to be controlled is the rotational speed of a rotating body, such as a roll in a printer, the digital feedback output signals are typically provided in the form of digital pulses which are outputted from an optical encoder. The digital pulses cannot directly be used by the PC, but rather must be converted to some form of other digital signal which can be readily interpreted and utilized by the PC. The process of converting the digital feedback pulse train to some other form of digital signal induces errors and noise into the signal which is used as feedback to the control system. Such errors and noise are not desirable.
What is needed in the art is a PID control system which allows the feedback signals from a target system to be more quickly and accurately used by the PIED control system without inducing noise into the system.